The present invention relates to mixtures of fluorescent whitening agents based on various isomers of cyano-substituted 1,4-bis-styrylbenzenes.
Fluorescent whitening agents are often used in the form of mixtures of two or more components, since such mixtures may exhibit a higher degree of whiteness than that of the sum of the individual components alone.
Thus, for example, GB 2200660 describes such mixtures although the composition is restricted by the method of preparation, whilst U.S. Pat. No. 5,695,686 describes similar asymmetric mixtures containing further isomers again due to the process of preparation. Furthermore, DE 19609956 describes extremely complex mixtures containing up to five different isomers of the dicyano-substituted distyryl benzenes.
The constitution of such mixtures of the dicyano-substituted distyryl benzenes is important not only in regard to their whitening effects, but also with regard to the shade, which may be more or less reddish or greenish, the desirability being a matter of utmost importance to the end user.
It has now, surprisingly, been found that particularly high degrees of whiteness in especially desirable shades are obtained from mixtures of fluorescent whitening agents comprising 20 to 70% by weight of a compound of formula 
30 to 80% of a compound of formula 
0.5 to 5% of a compound of formula 
Furthermore, mixtures comprising 50 to 70% by weight of the compound of formula (1), 30 to 50% of the compound of formula (2) and 0.5 to 5% of the compound of formula (3) are of particular interest, whilst mixtures comprising 55 to 70% by weight of the compound of formula (1), 30 to 45% of the compound of formula (2) and 0.5 to 3% of the compound of formula (3) are especially suitable and, preferably, mixtures comprising 58 to 62% by weight of the compound of formula (1), 38 to 42% of the compound of formula (2) and 0.5 to 3% of the compound of formula (3) should be used.
The mixtures of the invention are prepared by condensing terephthalaldehyde with a 4-dialkylphosphonomethyl benzonitrile and further condensing the resulting 4 cyano-4xe2x80x2-formylstilbene obtained as intermediate with a 2- or 3-dialkylphosphonomethyl benzonitrile according to the following scheme: 
whereby R represents methyl, ethyl, propyl or butyl, preferably methyl or ethyl.
The initial condensation of terephthalaldehyde with a 4-dialkylphosphonomethyl benzonitrile is carried out in a lower alcohol, for example methanol, ethanol, n- or isopropanol or n-, sec.- or tert.-butanol, preferably methanol, as solvent and in the presence of an alkali metal hydroxide such as lithium, potassium or sodium hydroxide, preferably potassium hydroxide. During the course of this condensation, small amounts, i.e. up to 5%, of 4,4xe2x80x2-dicyano-(1,4-bis-styryl)benzene are produced as a by-product, which is then advantageously present in the final mixture. After reaction, the 4 cyano-4xe2x80x2-formylstilbene precipitates from the reaction mixture and is isolated by filtration.
The second condensation step is carried out in a dipolar aprotic solvent such as dimethyl-formamide, dimethyl sulphoxide, N-methyl pyrrolidone or tetramethyl urea, preferably dimethylformamide, in the presence of strong base such as a sodium or potassium C1-C5-alcoholate, especially sodium methylate.
Further objects of the present invention are the use of the mixtures of the three compounds of the formulae (1) to (3) for whitening synthetic fibres, in particular polyester fibres, said compositions containing a mixture comprising 20 to 70% by weight of a compound of formula 
30 to 80% of a compound of formula 
0.5 to 5% of a compound of formula 
Furthermore, mixtures comprising 50 to 70% by weight of the compound of formula (1), 30 to 50% of the compound of formula (2) and 0.5 to 5% of the compound of formula (3) are of particular interest, whilst mixtures comprising 55 to 70% by weight of the compound of formula (1), 30 to 45% of the compound of formula (2) and 0.5 to 3% of the compound of formula (3) are especially suitable and, preferably, mixtures comprising 58 to 62% by weight of the compound of formula (1), 38 to 42% of the compound of formula (2) and 0.5 to 3% of the compound of formula (3) should be used.
As is customary with mixtures of fluorescent whitening agents, the individual components can be processed to the commercial form by dispersing them in a liquid medium, preferably water. This can be done by dispersing the individual components and then combining the dispersions so obtained. However, it is also possible to mix the individual components together in substance and then to disperse them jointly. The dispersing operation is carried out in a conventional manner in ball mills, colloid mills, bead mills or the like.
The present invention thus further provides brightener compositions containing water and, in each case based on the weight of the formulation, from 3 to 25% by weight, preferably from 5 to 15% by weight of the above defined fluorescent whitening agent mixture and also 0 to 60%, preferably 5 to 50% by weight, of auxiliaries.
Suitable auxiliaries include, for example, anionic or non-ionic dispersants from the class of ethylene oxide adducts with fatty alcohols, higher fatty acids or alkyl phenols or ethylenediamine ethylene oxide-propylene oxide adducts, copolymers of N-vinylpyrrolidone with 3-vinylpropionic acid, water retention aids, such as ethylene glycol, glycerol or sorbitol, or biocides.
The mixtures of this invention and the compositions containing them are suitable for whitening textile materials made from synthetic fibres, in particular, those made from linear polyesters. However, these mixtures and compositions can also be used for whitening blends that contain linear polyesters.
The mixtures of this invention are applied by the methods normally employed for the application of fluorescent whitening agents, for example, by the exhaust dying process in dying machines or by pad-thermofixation. The treatment is conveniently effected in an aqueous medium in which the compounds are present in finely particulate form as suspensions, microdispersions or, as the case may be, solutions. If appropriate, dispersants, stabilisers, wetting agents and other assistants can be added during the treatment. The treatment is normally carried out in the temperature range from about 20xc2x0 C. to 140xc2x0 C., preferably 110 to 130xc2x0 C., for example, at the boiling temperature of the bath or in the proximity thereof. Where the mixtures are applied by the pad-thermofixation process, the thermofixing is preferably carried out at a temperature of between 170 and 200xc2x0 C.